This invention relates to apparatus for annealing bare wire by resistively heating it, and in particular to improved annealing apparatus for wires. More broadly, however, the invention relates to a free running, low friction pulley assembly for making electrical contact to strand material.
In the prior art, it has been known to anneal bare wire by resistively heating it. In general, the apparatus for carrying out this annealing process has included at least two contact pulleys which serve as electrical contacts to the wire passing around them to cause the annealing current to flow in the section of wire between the pulleys. In the prior art, the contact pulleys have been made of steel or other relatively heavy metal which creates a substantial moment of inertia and rolling resistance. In addition, the brush assembly used with prior art annealing devices to make electrical contact to the pulleys, has also contributed a substantial amount of drag to the pulley assembly. For this reason, in the prior art, the pulleys have, of necessity, been driven by external driving means at a peripheral speed which substantially approximates the wire speed as it moves through the annealer. If the peripheral pulley speed and the wire speed are not exactly synchronized, a limited amount of slip between the wire and the pulley occurs. This slip can, in some cases, be tolerated, but it does cause substantial wear on the pulley which necessitates its repair at intervals more frequent than desired. In other cases, such as when plated wire is being annealed, any slip between the wire and the annealer pulleys, actually causes the plating to be stripped off. It is clear, therefore, that slip cannot be tolerated whenever plated wire is being annealed. It is also possible to synchronize the wire speed and peripheral pulley speed by using an electric control circuit to control the speed of the pulley driving motor, as shown in U.S. Pat. No. 3,697,335, or by providing a magnetic clutch between the driving shaft and the pulley wheel, as shown in U.S. Pat. No. 3,530,274.
In order to overcome the problems associated with prior wire annealing apparatus, the device disclosed in U.S. Pat. No. 3,989,923 was developed. This device utilizes free running (non-driven) contact pulleys which are rotatably mounted on a fixed shaft by low friction bearings. In addition, this device utilizes low torque electrical contacts. While this device operates reasonably well for its purpose, it is desirable to provide a contact pulley which exhibits less friction, to make the annealer as ideal as possible.